More particularly, the invention relates to the devices used for holding and turning the tires so that the operations of visually inspecting the surfaces thereof can be carried out.
Visual inspection is widely used in the tire manufacturing process and even more commonly relies on the skill of the operators tasked with checking for the absence of visible imperfections at the surface of the tires in order to ensure compliance thereof.
However, with the advances in the computing power of computer-based means, tire manufacturers are developing automatic inspection means to assist the operators tasked with the visual inspection. To this end, it is possible to use an inspection device comprising lighting means and cameras which are positioned in such a way as to scan the exterior and interior zones of the lateral beads and of the tread of the tire that is to be inspected. The viewing field of each camera is angularly limited. In order to obtain complete images of the inside and outside of the tire the tire has to be turned about its axis with respect to the lighting means and with respect to the cameras. The digital images obtained are then processed and compared against reference images in order to determine whether there might be any surface and appearance anomalies in the tire. For further details, reference may for example be made to patent applications EP-A2-1 959 227, EP-A1-2 023 078 and EP-A1-2 172 737.
In order to carry out such an inspection, it is appropriate to use a device that holds the tire accurately as it is being turned. Document U.S.2008/0066532 discloses a drive device comprising a plurality of pairs of hooks which press against the internal faces of the lateral beads of the tire so as to space them from one another. The hooks are able to move between an engaged position for holding and turning the tire and a folded position for allowing the tire to be introduced and removed.
That device has the major disadvantage of not allowing images to be taken of the internal faces of the lateral beads of the tire in the zones against which the hooks bear. Thus, these hidden zones cannot be inspected without having first angularly repositioned the tire with respect to the hooks.
In order to overcome this disadvantage, the applicants have developed a holding and turning system comprising a centring ring for centring a first lateral bead of the tire, locking hooks for locking the said bead to the ring, two interior holding rollers mounted to press against the internal face of the second lateral bead of the tire, and an external holding roller pressing against the external face of the second bead situated circumferentially between the interior holding rollers. For further details, reference may be made to patent application WO-A1-2011/113711.
The use of the internal and external holding rollers allows an interior image of the tire to be captured with high geometric precision. In order to minimize the movements of the second lateral bead of the tire during the image-capture operation, the system also comprises lift rollers mounted to press against the internal face of the second bead so as to turn the said bead up axially in a circumferential segment that complements the segment occupied by the internal and external holding rollers.
Such an axial turning-up of the second bead towards the outside does, however, prevent an external image of the tire from being captured simultaneously in so far as the bead and the associated side wall are too deformed.
It is thus necessary to provide an additional special-purpose holding system able to hold the tire in the inflated state in order to obtain an exterior image of the tire with good geometric precision. This appreciably increases the cycle time required for visually inspecting the tire and the associated cost.